Project Summary Ataxic dysarthria, associated with cerebellar disease, represents approximately 10% of all motor speech disorders. Abnormal speech rhythm and articulation are common in ataxia. As a result, speech intelligibility and naturalness may be severely impaired. Little empirical evidence is available to drive effective speech therapy for ataxia dysarthria. The hypothesis that propels this project is that hand gestures that convey rhythmic cues (beat gestures) have the potential to augment abnormal speech rhythm and articulation through entrainment. In task dynamic theory, rhythmic entrainment is the time-varying spatiotemporal task-specific coordination among structures or processes. But speech rhythm is language-dependent, and so it is uncertain whether native (L1) and nonnative (L2) speakers can exploit rhythm similarly. Moreover, the potential for entrainment in the presence of sensorimotor impairment is uncertain. The long-term goal of this project is to develop rehabilitation strategies, grounded in task dynamic theory, that capitalize upon rhythmic entrainment to improve intelligibility and speech naturalness in bilingual speakers with dysarthria. Rhythmic entrainment of hand and articulatory gestures is well documented in monolingual speakers. No studies have explored rhythmic entrainment of beat gestures in L2 speakers with or without dysarthria. Task dynamic theory holds that both rate and rhythm are task-specific control parameters that influence behavior. Our preliminary data suggest that effort is another parameter. The objectives of this proposal are to determine the effect of rhythmic entrainment on intelligibility in L2 speakers with ataxic dysarthria, and the extent to which rate and effort are control parameters that influence entrainment. The specific aims of this project are to determine the effect of three rates of beat gestures, the effect of increased effort (realized as clear speech), and the interaction effect, on intelligibility, speech naturalness, and acoustic metrics in L1 and L2 speakers with and without ataxic dysarthria. Data will be obtained using a single-case experimental design. Baseline measures (Phase A) will be followed by training of beat gestures coordinated with speech (Phase B) using a randomized, multiple- baseline design replicated across 12 talkers. Probes on outcome measures (perceptual and acoustic) will be gathered at each session in conversational and clear speaking styles in three beat gesture rate conditions: no gesture and two imposed rates. The 12 talkers will be equally divided into L1 English and L2 English (L1 Spanish) talkers, and those with and without ataxic dysarthria. The multiple baseline, replicated AB design with the start of the B phase (training) staggered across participants is the strongest of the single-case experimental designs used to investigate the functional relationship between treatment and outcome scores. Rhythmic entrainment in L1 and L2 speakers with dysarthria is an unexplored area of study that offers a unique opportunity to develop novel rehabilitation strategies, grounded in task dynamic theory, for a large, underserved population.